Aliphatic lactones are particularly useful, especially in foodstuffs, because of their organoleptic properties. These materials have high flavor value due to their extremely low odor thresholds which average about 0.1 ppm.
While numerous methods are known for synthesizing lactones, especially from glycerides, higher molecular weight fatty acids and short chain functional group containing aliphatic compounds, many of the lactones are naturally occuring. The gamma-lactones occur mainly in plants, and the delta-lactones in animals.
An extensive literature survey relative to various lactones has been prepared by G. Ohloff and appears in Fortschritte d. Chem. Org. Naturstoffe, Volume 35, pages 431-527 (1978).
The present invention provides an improved method for making certain aliphatic lactones which are useful in small concentrations in food products as flavor and odor in parting materials. Moreover, these compounds have utility as intermediates in the preparation of still other odor and flavor imparting materials.
Lactones also have utility as solvents for polymers and copolymers of acrylonitrile. Reference may be had to the patent to Ham, U.S. Pat. No. 2,503,200 in this respect.
As indicated above, various methods are known for the preparation of aliphatic lactones. Reference may be had to U.S. Pat. No. 2,420,250 for one method of preparing gamma-valerolactones. According to this process, a 1,4-pentanediol is heated with a copper chromite catalyst under reflux conditions until the evolution of hydrogen ceases. The resulting reaction mixtures then distilled under reduced pressure to recover gamma-valerolactone.
According to U.S. Pat. Nos. 3,992,417 and 4,175,089, to Dessau et al, gamma-butyrolactones are formed by reacting an olefin with a compound containing a carboxylate group having at least one hydrogen atom on the alpha carbon atom in the presence of an ion of manganese, cerium or vanadium, the ion being in a valency state higher than its lowest valency state.
U.S. Pat. No. 2,569,064 discloses the preparation of gamma-lactones by heating a 2,2,4-trihalogenoalkanoic ester in the presence of catalyst such as zinc chloride, boron trifluoride, etc.
U.S. Pat. No. 2,968,568 discloses the preparation of butyrolactones by reacting bromoacetic acids and derivatives thereof with alpha olefins in the presence of a catalyst, preferably a free radical catalyst.
The present invention differs from the prior art in that the starting material is an unsaturated ketone which is alkylated by means of an organometallic compound, such as a Grignard reagent, to provide an alcohol containing an olefinic group. The resulting product is then oxidatively cleaved and cyclized to produce the lactone. The process is applicable to gamma and delta-lactones. PG,4